Cyst

A cyst is a closed sac having a membrane separating it from nearby tissues. Cysts may contain fluids such as cerebrospinal fluid (CSF), necrotic (dead) tissue that is semi-solid or hemorrhage (blood products). A collection of pus is called an abscess, not a cyst. Relative to the pituitary gland and brain, the most common cystic problems include arachnoid cysts, cystic craniopharyngiomas, Rathke’s cleft cysts and hemangioblastomas.